Empirically it is quite easy to validate that the "20x" plan is misleading and only give you twice the weekly limits of the "5x" plan, and many people on r/ClaudeAI, etc can verify that.

Anthropic is also the one often playing games with:

* The "+30% tokens" tokeniser, alongside also gating token counting behind an API (versus the MIT tiktoken for OpenAI), so who knows if it's really a new tokeniser or of it's just a disguised price increase.

* Prompt injections appended to API (not just Claude.ai or Claude Code!), such as <ethics_reminders>, or LCRs (long conversation reminders), which you never asked but still pay for with expensive API. You can detect this because your input_tokens, as reported by the Messages response, sometimes don't match, and are higher than your actual input.

(Alternatively, for testing purposes, create a tool like `telemetry_log_anthropic_reminder` or something and instruct your system prompt to require Claude to call the tool anytime it detects any Anthropic/Claude reminder masquerading in the user input -- mostly reliable; but misses some reminders).

In particular, the long conversational reminders, when incorrectly triggered by a classifier and (almost silently, unless you track tokens) appended to an API / agentic coding session, can ruin your agent's performance; and it often fires repeatedly once the classifier kicks in.

If you're using Anthropic API, you need to set up metrics/logging for how often they are appending things to your prompt without your knowledge.

So far I have not empirically observed prompt injection by the OpenAI API, only Anthropic APIs.